Along with the invention of the wheel, the invention of rope constitutes one of the most useful and significant technical advances in the history of mankind.
Rope makes possible the performance of myriad tasks previously impossible: lowering anchors to the seabed to moor ships, raising and lowering heavy objects on land, those aspects of alpine sports and cave climbing which require ropes, civilian and military rappels, rescue activities where individuals must be lowered to safety, etc.
A requirement common to many of these activities is the ability of the rope handler to govern the speed of descent of an individual or heavy object attached to the rope he is handling.
Frictional brakes for use with rope or the like have been developed to aid the rope handler in lowering a heavy object. 0n ships the anchor line is wound around a capstan barrel several times so that when the rope is held taut around a rotating capstan, the rope is taken in or let out by virtue of the friction between the rope and the capstan barrel.
The bar rack was developed to provide a smaller and more portable frictional rope brake. Referring to FIGS. 1-8 we can observe a bar rack 2 and its method of operation.
FIG. 1 is a front isometric view of bar rack 2, comprised of links 12 free to slide along loop rod 6 and threaded rod 4. The links 12 are constrained at one end by nut 5 threaded onto threaded rod 4 and loop 8, and at the other end by half circle 10.
FIG. 2 is a front plan view of bar rack 2.
FIG. 3 is a cross sectional view of a link 12 taken at section A--A of FIG. 2. Link 12 has holes 16 through which loop rod 6 passes and slot 14 which frictionally admits threaded rod 4.
FIG. 4 illustrates how link 12 may rotate about loop rod 6 in order to facilitate the installation of a rope 24 in bar rack 2 as depicted in FIGS. 6-8. Link 12 may be re-engaged with threaded rod 4 by rotating link 12 about loop rod 6 as shown by arrow 18 and frictionally snapping threaded rod 4 into slot 14.
FIG. 5 illustrates a typical use scenario for bar rack 2. Rope handler 22 has installed rope 24 into bar rack 2 and is lowering an individual being rescued 28 off building 20.
FIGS. 6-8 show how bar rack 2 is positioned during a lowering operation and then re-positioned so as to be ready for use in the next lowering operation.
FIG. 6 depicts bar rack 2 ready to be used for the first lowering operation: rope 24 is installed on bar rack 2; bar rack 2 is suspended by means of loop 8. The object to be lowered would be attached to rope end 23 and the rope handler would grasp the part of rope 24 having rope end 25.
The rope handler now allows rope 24 to travel through bar rack 2 until we have the situation depicted in FIG. 7: assuming a long enough rope 24, the object being lowered attached to rope end 23 is now at the desired height and little rope remains between bar rack 2 and rope end 25. The weight attached to rope end 23 may now be removed and bar rack 2 readied for the next lowering operation.
In order to lower the next weight, bar rack 2 must be rotated end for end and suspended by means of half circle 10 as depicted in FIG. 8 . A new weight to be lowered may now be attached to rope end 25, and the rope handler grasps that portion of rope 24 having rope end 23 and allows rope end 25 to descend by permitting rope 24 to travel through bar rack 2 as before.
A number of problems exist associated with using the bar rack for a series of lowering operations.
First, between uses, the rope handler must detach bar rack loop 8 from its attach point, rotate bar rack 2 end for end, and then attach half circle 10 to the attach point. In a fire rescue situation where seconds count this delay may be costly.
Second, wherever handling is involved, the danger of dropping the item being handled exists. If the rope handler were to drop the bar rack, further delays would occur, not to mention the hazard to individuals below.
Third, it may be physically impossible for the rope handler to rotate the bar rack due to the combined weight of the bar rack and rope--1000 feet of rope can weigh over 150 pounds.
Fourth, when bar rack 2 is suspended by means of half circle 10 as depicted in FIG. 8, the danger exists that one or more links 12 may become disengaged from threaded rod 4 due to rope movement. This link disengagement would constitute a catastrophic failure of the bar rack if all links were to snap free: the individual being rescued 28 would free fall down to the surface below. In the case of a high rise building fire rescue operation this fall could be fatal.
Finally, no provision exists in the bar rack design to quickly and automatically adjust the amount of friction imparted the rope by the bar rack: lowering a heavy weight requires more effort from the rope handler than a light weight. The work associated with lowering a series of heavy people to safety combined with the added chore of having to lift the bar rack, rotate it end for end, and then re-suspend between each lowering operation contributes to rope handler fatigue, the possibility of error, and may place the outcome of the rescue in jeopardy.